1. Field of the Invention
This invention relates to tow cables for towed acoustic arrays.
2. Discussion of the Background
Conventional towed arrays, or streamers, have consisted of towing cable, which must be negatively buoyant to achieve submersion to the required depth, a forward Vibration Isolation Module (VIM) to minimize the transmission of mechanical vibration from the tow cable to the acoustic array, an array of acoustic (and non-acoustic) sensors, and an aft VIM to minimize transmission of vibration from the `flapping tail` forward to the acoustic array.
This invention relates to the construction and form of the tow cable which links the towing vessel to the head of the acoustic streamer and, through its density, determines the depth at which the streamer is towed.
Conventional tow cables have typically comprised a multicore inner portion, surrounded by several layers of helically wound steel armoring which provides the required density, tensile strength for towing, and extreme robustness to resist the rigors of handling during deployment and retrieval operations. Regretfully, this construction has also brought disadvantages, including the limitations of limited flexibility (large bend radius), a relatively large diameter (to achieve the target specific gravity of 3 or more) and, with the normal circular section, a low resistance to excitation into strumming by periodic vortex shedding--a problem usually treated by the addition of difficult-to-handle `flags` along the cable length. The dominance of the cable's mechanical characteristics by the steel armoring results in very little internal damping to attenuate any periodic cable strumming that is excited.